1. Field of the Invention
This invention relates generally to electron beam exposure devices and more particularly, to an improved mounting ring for supporting the X and Y axis interferometers in a stabilized manner resistant to the detrimental effects of both thermal and vacuum pressure conditions prevalent in the chamber of the device.
2. Description of the Prior Art
The stability of the various components employed in electron beam devices has long been addressed, in view of the thermal deviations evident within the vacuum chamber. The firm Schott & Gen. of Mainz, Germany developed a glass ceramic composition, registered under the trademark ZERODUR and which exhibits a high degree of thermal stability. U.S. Pat. No. 4,777,371 issued Oct. 11, 1988 to Baute is directed to a specific composition of this ZERODUR product wherein the crystalline phase has a negative thermal expansion, while that of the glass phase is positive whereupon the linear thermal expansion of the glass ceramic is largely compensated as a whole. By regulating the phases of the ZERODUR constituents, Baute proposes using his glass ceramic in the formation of the apparatus support components comprising the substrate supports for the masks, the receiving table or stage and its support arm and the substrates for the adjusting mirrors of the receiving table. Although this patent reference teaches the use of thermally stable material in the construction of various components in an electron beam apparatus, there is no suggestion therein of the present development wherein the upper wall of the vacuum chamber is protected by a ring of glass ceramic, with the interferometers being mounted thereupon, in order to maintain steady alignment of the optical axes of the interferometers, notwithstanding thermal variations as well as the influence of vacuum pressures within the apparatus vacuum chamber.
An X-ray lithography apparatus is shown in U.S. Pat. No. 4,694,477 issued to Siddall on Sep. 15, 1987 and is directed to means for carrying out single stage alignment which in this reference is produced by a plurality of piezoelectric transducers (PZTs) and although flexure strips are employed in this reference, they are connected to a stage plate. This is contrary to the present invention wherein alignment control is achieved through the use of interferometers and flexure mounts serve in the attachment of a glass ceramic ring to which the interferometers are affixed.
U.S. Pat. No. 4,703,181 issued Oct. 27, 1987 to Swall et al. depicts means to control thermal drift in an electron microscope and wherein movement of a specimen holder is regulated by an arrangement including a tube containing a close fitting rod. Control of drift in the present system is not by a mechanical element engaging a specimen holder but rather by interferometers attached to a glass ceramic ring underlying the upper wall of a vacuum chamber.
Stabilizing means for a workpiece in an electron beam apparatus is shown in U.S. Pat. No. 4,782,236 issued Nov. 1, 1988 to Chitayat and wherein spring rods and stabilizing posts are employed. This is in complete contrast to the construction as advanced herein and referenced above.
The particle beam lithography apparatus taught in U.S. Pat. No. 4,818,838 issued to Young et al. on Apr. 4, 1989 relates to means for preselecting a gap size between the tip of a vacuum seal apparatus and the workpiece surface and maintaining this gap during workpiece processing. This control is achieved through the use of gas bearings as opposed to the instant proposal wherein a glass ceramic ring of particular construction and location serves to support interferometers in an environment which is normally hostile to thermal variations and the influence of vacuum pressure.
A support mechanism for use in apparatus analogous to the present technology is advanced in U.S. Pat. No. 4,969,168 issued Nov. 6, 1990 to Sakamoto et al. and describes means for supporting a wafer upon a chuck. Initially, the wafer is attracted by the application of a vacuum and thereafter the support is by electrostatic attraction, a vast departure from the present system which concerns the use of a specific ring to underlie the upper wall of a vacuum chamber and serve to support interferometers.
U.S. Pat. No. 5,025,165 issued Jun. 18, 1991 to Chen et al. relates to an electron beam apparatus and specifically addresses alignment inaccuracies. Rather than providing means for insuring maintenance of the optical alignment of interferometers as taught herein, the Chen et al. device is directed to the inclusion of a particular reference mark(s) on the semiconductor body used in concert with an electromagnetic source and detector, both located exterior of a vacuum chamber.
The addressing of thermal stability in an electron beam apparatus will be found in U.S. Pat. No. 5,136,166 issued Aug. 4, 1992 to Young wherein, a thermally stable magnetic deflection assembly is formed with a plurality of magnetic coils and intermediate non-metallic thermally stable material. The instant improvement, on the other hand, is directed to thermal and vacuum resistant construction all within the working vacuum chamber, rather than in an electron column.
U.S. Pat. No. 5,214,290 issued to Sakai on May 25, 1993 relates to an electron beam lithography apparatus and is specifically directed to a workpiece supporting table and X-Y axis shifting mechanism therefore, unlike the current invention which is concerned with the inclusion of a glass ceramic ring for support of interferometers.
U.S. Pat. No. 5,280,178 issued to Engelen et al. on Jan. 18, 1994 concerns a charged particle beam apparatus and depicts a specimen holder comprising a resilient ring, as used in an electron microscope, unlike the instant development concerning a ring structure of specific composition for supporting interferometers to resist alignment drift due to thermal and vacuum pressure influences.
None of the above inventions and patents, taken either singly or in any combination, is seen to even remotely suggest or describe the instant invention as claimed herein.